1. Field of the Invention
The technical scope of the present invention is that of laying methods and devices for pipes intended to transport fluids such as pipelines for the transport of hydrocarbons.
2. Description of the Related Art
The Pipe-in-Pipe concept is well known and is namely presented in the form of straight sections assembled end to end. Reinforcement rings, named bulkheads, are evenly spaced along the pipe between two sets of sections so as to link the two casings axially.
Each section comprises an inner pipe arranged coaxially in an outer pipe. A thermal insulating system additionally enables the two pipes, able to slide with respect to one another, to be positioned. The inner pipe is linked, by welding, to the inner casing of the portion of pipe already in place and then the outer pipe is linked by welding to the outer casing. The bulkheads rigidify the pipe and compartmentalize the annulus into several parts each extending for a length of, for example, 500 m to 3 km. The bulkheads are thus typically spaced with respect to one another by 500 m to 3 km.
The pipes constituting each section are made of metal and the positioning and thermal insulation system comprises, for example, flexible panels of a material that is sufficiently resistant to bear the weight of the pipes, such as IZOFLEX® or other material incorporating pyrogenic silica. The positioning and thermal insulation system may also comprise spacers, for example made of a polymer, wood or metal, to ensure the concentric alignment as well as a filling material to ensure the thermal insulation. Each section extends, for example, for a length of around 12 m, 24 m, 48 m, 72 m or 96 m.
The fact of positioning insulating material between the two pipes advantageously thermally insulates the inner pipe. One problem is, however, that for the thermal insulation to be optimal, the pressure must be reduced in the space in which the insulation is arranged. However, this operation takes time because of the high degassing times for the materials and surfaces facing the annulus space. Thus, when the sections are laid, by a pipe-laying ship using the S-lay or J-lay method, the pressure reducing operation is generally omitted because of the lack of available time when the pipeline is being laid.
There is thus a need to improve the laying of pipe-in-pipe pipelines constituted by straight sections with an annulus that is compartmentalized by bulkheads so as to provide better thermal insulation.